Printer manufacturers provide printing devices that measure a remaining amount of ink or toner (e.g., consumable supplies) in a toner cartridge toner cartridge, and communicate this information to a user. For example, a user may desire a printing device to provide information on whether there is enough toner left to print, for example, a 100 page document. So a basic problem facing printer manufacturers is accurately determining how much ink or toner is actually left in a toner cartridge.
For laser printers, “pixel counting” estimation methods are often used to measure a remaining amount of toner by tracking an “on time” of a video signal waveform used to charge an optical photo conductor drum. The photo conductor drum is written on by, for example, a laser, changing a charge on the drum at various locations to attract toner and transfer it to a sheet of paper. A signature of the laser of the drum is then used to determine how much toner has been attracted. However, the relationship between laser signature, and an amount of toner used, is a function of factors such as drum age, ambient humidity, ambient temperature, and other factors. Thus, “pixel counting” techniques are not highly accurate. Other techniques may simply count pages, measure contone values of the input image or use a light source and photocell receptor to estimate a remaining fill level of toner or ink in a toner cartridge. However, these techniques are also not highly accurate. Generally, factory measurements relating ink or toner usage are preformed, and the product is shipped with a relationship function programmed into firmware that provides an estimation of a remaining number of pages that can be printed based on current usage.